Comparison of agar gel immunodiffusion test, enzyme-linked immunosorbent assay and western blotting for the detection of BLV antibodies

Triple Immunochromatographic System for Simultaneous Serodiagnosis of Bovine Brucellosis, Tuberculosis, and Leukemia

An immunochromatographic test system has been developed for the simultaneous rapid multiplex serodiagnostics of bovine brucellosis, tuberculosis, and leukemia. The test system is based on the use of a conjugate of gold nanoparticles with the chimeric protein Cysteine-A/G and three analytical zones with immobilized pathogen antigens: Brucella abortus lipolysaccharide, recombinant proteins MPB64 and MPB83-MPB63 of Mycobacterium bovis, and recombinant protein p24 of the bovine leukemia virus. Prototypes of the test system were tested on 98 samples of sera from healthy and infected animals. The diagnostic sensitivity of the developed test system was 92% for brucellosis, 92% for tuberculosis, and 96% for leukemia. False positive test results were not observed.

Development of an indirect ELISA based on recombinant capsid protein to detect antibodies to bovine leukemia virus

Serological testing and culling infected animals are key management practices aiming eradication of bovine leukemia virus infection. Here, we report the development of an indirect ELISA based on BLV recombinant capsid protein (BLVp24r) to detect anti-BLV antibodies in cattle serum. The BLVp24r was expressed in Escherichia coli and purified by affinity chromatography, and then used to set up the ELISA parameters. The Polysorp^® plate coated with 50 ng of antigen/well and bovine serum diluted 1:100 gave the best results during standardization. Using sera from infected and non-infected cattle we set up the cutoff point at 0.320 (OD_450 nm) with a sensitivity of 98.5% and specificity of 100.0%. Then, we tested 1.187 serum samples from dairy (736 samples) and beef cattle (451 samples) with unknown status to BLV. We found that 31.1% (229/736) and 9.5% (43/451) of samples amongst dairy and beef cattle, respectively, had IgGs to BLV. The rate of agreement with a commercial competitive ELISA was 84.3% with a κ value of 0.68. Thus, our BLVp24r iELISA is suitable to detect BLV infected animals and should be a useful tool to control BLV infection in cattle.

Relative sensitivity and specificity of agar gel immunodiffusion, enzyme immunosorbent assay, and immunoblotting for detection of anti-bovine leukemia virus antibodies in cattle

Three serologic methods for the detection of antibodies to bovine leukemia virus (BLV) were compared using the sera of 140 dairy cows. A widely used commercial agarose immunodiffusion screening assay and a commercial antibody capture enzyme immunosorbent assay were compared for sensitivity and specificity with immunoblotting as the standard. The immunoblot utilized the same antigen preparations that were provided in the commercial kits. The agarose immunodiffusion and the enzyme immunosorbent assay were comparable in the number of positive animals detected. However, the commercial screening kits failed to detect 39% (agarose immunodiffusion) and 35% (immunosorbent assay), respectively, of the animals determined serologically positive by immunoblot. These findings corroborate those of some other groups and emphasize the need for more sensitive tests to identify BLV positive cattle for culling or separation in order to create BLV-free herds.

Comparative study of PCR as a direct assay and ELISA and AGID as indirect assays for the detection of bovine leukaemia virus

The choice of a diagnostic method depends on the characteristics of the herd to be analysed. Two herds with different prevalences of enzootic bovine leukaemia were chosen to study the concordance between agar gel immunodiffusion (AGID), enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) methods. PCR, an increasingly used virological method, was performed with four sets of primers, amplifying different genomic regions (env, pol and tax), from DNA extracted either from peripheral blood monocytes (PBMCs) or milk leucocytes. The highest percentage of positive animals was obtained using PCR performed with DNA extracted from PBMCs using primers which amplified either env or pol, followed by PCR using PBMCs and primers which hybridized with tax, then ELISA using serum and finally AGID. The results of PCR were more consistent with PBMCs than when milk leucocytes were used.